1. Field of the Invention
This invention relates to a process for the selective catalytic dehydration of n-butanol or iso-butanol (collectively referred to as butanol in this application) to mixed butylenes including 1-butylene, iso-butylene, and cis- and trans-2-butelens (herein collectively referred to as butylenes) using an improved technology of reactor design and configuration wherein the reactor train is comprised of a multi-stage single reactor vessel or multiple reactor vessels wherein each stage and/or vessel has different length, internal diameter, and volume than the other stages and/or vessels and in addition the stages and/or reactor vessels are connected in series or in parallel arrangement. Furthermore, this invention discloses an improved means of introducing the butanol feedstock and a heat carrying inert gas to the improved reactor train.
2. Related Information
The butylene isomers are important olefins which are extensively used commercially in the petrochemicals, chemicals, and oil industries. For example, isobutylene is the primary feedstock in the manufacture of viscous polybutenes which are extensively used in such diverse products as lubricating oils, anti-oxidants, additives, and other consumer goods. It is also a preferred raw material for alkylation process in the refining industry. Butylenes are also used in the production of synthetic rubber. Butylenes are primarily produced as secondary products from petroleum resources by the high temperature steam cracking of petroleum-derived feedstocks such as heavy naphtha, ethane/propane, or gas condensates. The economics of these processes are greatly influenced by the supply, availability, and price of crude oil and natural gas. In addition, the cracking processes produce large quantities of primary and valuable petrochemicals such as ethylene and propylene and other olefinic hydrocarbons. which have to be recovered and purified and therefore may not be ignored and disposed of as waste. The economics of the butylenes production by the steam cracking process thus require that these products be separated and recovered at very high purity suitable for downstream chemicals and polymer applications. This would require very complex processing scheme, high capital investment, and large energy consumption to separate, purify, and provide storage for all the primary and secondary products so that the steam cracking process can be economically justified. In addition, the success of the petroleum-derived butylenes requires that all the by-products be marketed to their respective end users. If a user of butylenes were interested in only producing butylenes and no other products, the cracking route is not a viable and profitable option. Furthermore, the conventional steam cracking produces large quantities of CO2 (carbon) which is a main component of the greenhouse gas emission. The mixed butylenes formed by the process claimed herein can be easily isomerized to the desired butylene isomer by any one of several processes in commercial operation.
The dehydration of butanol is a simple and attractive potential route to butylenes. Presently, there is no known commercial process for the catalytic dehydration of butanol. Recently, as the biofuels have attracted more attention globally, as prices of crude oil have increased and have become more unpredictable, and as petroleum supply sources have become more unstable and problematic, the butanol dehydration process is gaining interest as an alternative source for the production of chemical- or polymer-grade butylenes. In addition, with the threat to the environment and limited resources in some parts of the world, the butanol dehydration process is being increasingly competitive with the traditional steam cracking process. Furthermore, the sources of raw materials for butanol supply are expanding with a resultant decrease in the cost of butanol manufacture thus making it an attractive option for butylenes production.
The butanol dehydration reaction basically is characterized by the removal of a water molecule from butanol and as such is highly endothermic. A significant amount of heat (energy) is thus required to initiate and sustain the reactions to completion. Therefore, the choice of the reactor, its design, and configuration are critical aspects of managing the thermal events within the reactor and controlling the operating temperatures within the catalyst bed for an economical process.
Additionally, the economic production of butylenes by this process largely depends on the high conversion of butanol feedstock to avoid recovery and recycle of any unreacted butanol. It also requires high selectivity and yield of the butylenes product in order to avoid expensive separation and purification of the final product which is needed for chemicals and polymer applications. Furthermore, it is critical to limit the formation of by-products which will complicate the recovery and purification of the primary product and its downstream applications into high value-added chemicals and polymers.
Unlike the ethanol dehydration process to ethylene which has been the subject of many patents and developments and which has been commercially practiced for many years, there have been no known patents and/or technical articles on the dehydration process of butanol to butylenes.
While the chemistry of the dehydration of alcohols to olefins is well understood, the successful development of a process for selective dehydration of butanol to butylenes requires that a reactor design be developed consistent with the thermodynamics and kinetics of the dehydration reactions. Foremost, the reactions in this process are highly endothermic which require input of considerable amount of energy to derive the process. Therefore, the supply of heat, the management of the thermal processes, and the reactor temperature control constitute important considerations for optimum performance. One aspect of the present invention is a reactor disclosure to address these issues.
With regard to alcohol dehydration reactors which have been proposed and developed in the past, several patents stand out. U.S. Pat. No. 4,134,926 discloses a fluidized bed reactor concept for the dehydration of ethanol to ethylene wherein a portion of the dehydration catalyst is continuously withdrawn from the reactor chamber and regenerated with air in a second fluid-bed regenerator. The hot regenerated catalyst is then mixed with fresh make-up catalyst and recycled back to the primary reactor to provide the endodermic heat of reaction. This reactor concept has not found commercial application due to the complexity of the process, the handling and recycle of large quantities of solid catalyst, and continuous replacement of the lost catalyst because of attrition.
U.S. Pat. No. 4,232,179 describes a reactor train invention in which multiple, adiabatic reactor vessels are connected in series and/or parallel arrangement for dehydration of ethanol to ethylene. This patent further teaches the use of a sensible heat carrying fluid such as steam mixed with the alcohol feedstock prior to feeding to individual reactors. Each reactor is packed with a solid catalyst. The energy required for the reactions is supplied by a fired heater wherein both alcohol feedstock and steam are heated to very high temperatures needed for the reactions to proceed to completion in each reactor stage. This feature, being similar to British patent 516,360, can also result in lower selectivity and yield of the primary product and the formation of problematic by-products. In addition, no distinction is made in this disclosure as to the relative sizes of each reactor and the catalyst bed within that reactor with respect to other reactors and/or catalyst beds which make up the reactor train.
U.S. Pat. No. 4,396,789 teaches an invention which is basically similar to U.S. Pat. No. 4,232,179 with the exception that the reactor train is designed to operate at a design pressure of between 20 and 40 atmospheres. The patent claims that such high pressure operation will simplify the purification of the crude olefin product during the subsequent cryogenic distillation to produce high quality olefin for downstream chemicals/polymer applications.
In all the above processes, the dehydration catalyst is subjected to carbonization and rapid fouling as a result of direct exposure of the alcohol to the very high coil surface temperatures within the fired pre-heater. This practice would therefore entail less than optimum performance of the catalyst and would require frequent regeneration of the catalyst bed thus requiring downtime, loss of production, and shortened catalyst life.
It is the general object of this invention to maximize the utilization efficiency of the dehydration of butanol feedstock to butylenes product while minimizing the production of undesirable by-products. The specific goal of the present invention is to provide a novel, adiabatic reactor design and configuration to achieve the desired goals of the invention. Additionally, another goal of the present invention is to disclose an efficient process for carrying out the dehydration reaction. Furthermore, it is an object of the present invention to utilize the available streams normally found within a production facility or derived from the operation of the dehydration process carried out in the reactor. Other objects and benefits of the present invention will become apparent to those experienced in the art in the following sections.